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locking/mutex: Rework task_struct::blocked_on

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Track the blocked-on relation for mutexes, to allow following this
relation at schedule time.

   task
     | blocked-on
     v
   mutex
     | owner
     v
   task

This all will be used for tracking blocked-task/mutex chains
with the prox-execution patch in a similar fashion to how
priority inheritance is done with rt_mutexes.

For serialization, blocked-on is only set by the task itself
(current). And both when setting or clearing (potentially by
others), is done while holding the mutex::wait_lock.

[minor changes while rebasing]
[jstultz: Fix blocked_on tracking in __mutex_lock_common in error paths]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Connor O'Brien <connoro@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lkml.kernel.org/r/20250712033407.2383110-3-jstultz@google.com
This commit is contained in:
Peter Zijlstra
2025-07-12 03:33:43 +00:00
parent 25c411fce7
commit 44e4e0297c
5 changed files with 45 additions and 12 deletions
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9
kernel/locking/mutex-debug.c
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@@ -53,17 +53,18 @@ void debug_mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
{
lockdep_assert_held(&lock->wait_lock);
/* Mark the current thread as blocked on the lock: */
task->blocked_on = waiter;
/* Current thread can't be already blocked (since it's executing!) */
DEBUG_LOCKS_WARN_ON(task->blocked_on);
}
void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
struct task_struct *task)
{
struct mutex *blocked_on = READ_ONCE(task->blocked_on);
DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
DEBUG_LOCKS_WARN_ON(waiter->task != task);
DEBUG_LOCKS_WARN_ON(task->blocked_on != waiter);
task->blocked_on = NULL;
DEBUG_LOCKS_WARN_ON(blocked_on && blocked_on != lock);
INIT_LIST_HEAD(&waiter->list);
waiter->task = NULL;